1. Field of the Invention
The present invention relates to an ink cartridge for storing ink therein to be fed to an inkjet recording head and an inkjet recording apparatus having the ink cartridge mounted thereon.
2. Description of the Related Art
Various types of ink cartridge have been proposed. An ink cartridge is a liquid storage container storing ink therein for feeding the ink to an inkjet recording apparatus. Ink cartridges are roughly classified into three types as follows.
A first type is a so-called whole sponge type for retaining ink by arranging a capillary material, such as a sponge, within the entire internal space of the ink cartridge. A second type is a so-called whole raw ink type directly storing ink in a bag without using such a capillary material. A third type is a so-called semi-raw ink type in that one half of the ink cartridge is provided with the capillary material while the other half is provided with a raw ink chamber for directly storing ink within a casing.
In order to preferably feed ink to the recording head for ejecting the ink, in any of these types of ink cartridges, a configuration for adjusting holding power of the ink stored in the ink cartridge is important. Since this holding power is for leaving the pressure of an ink ejection part of the recording head negative relative to the atmosphere, the holding power is called a negative pressure.
In the whole sponge type mentioned above, ink is retained due to the characteristics of the capillary material and the negative pressure applied to the ink, so that this type has been adopted in various products.
However, in the whole sponge type, the amount of ink retained in the ink cartridge is small in ratio in comparison with the whole raw type. Also, since the negative pressure level and the flow resistance are increased just before ink is used up, the ink remains within the sponge, so that the available ink amount is smaller than the entire volume of the ink cartridge, i.e., the storing efficiency is small. Thus, a whole raw type ink cartridge is proposed in which a spring member is provided in an ink bag for urging the ink bag so as to maintain the bag at a negative pressure in order to increase the ink capacity per unit volume of the ink cartridge and also to achieve stable ink feeding (Japanese Patent Laid-Open No. H06-198904).
FIG. 6 is an exploded view of an ink cartridge having the configuration disclosed in Japanese Patent Laid-Open No. H06-198904, and FIG. 7 shows the interior of the ink cartridge being urged so as to maintain it under negative pressure.
An ink cartridge 10 shown in FIG. 6 includes a plastic frame 16 defining an open space serving as an ink reservoir. Within the open space of the frame 16, a pressure regulator 30 is accommodated for maintaining the interior at a negative pressure. On one side of the open space of the frame 16 is provided a flexible thin film 22 bonded to the plastic frame so as to close the one side of the open space. A hard cover plate 12 is bonded with an adhesive on the thin film 22 so as to cover it. On the other side of the open space is provided a flexible thin film 24 bonded to the plastic frame so as to close the open space. A hard cover plate 14 is bonded with an adhesive on the thin film 24 so as to cover it. Thereby, a flexible ink reservoir having a pressure regulator 30 accommodated therein is formed within the ink cartridge 10.
A tip portion 13 of the ink cartridge 10 is provided with an ink ejection nozzle arranged on the bottom end wall, to which a print head (not shown) is mounted and electrically driven.
The pressure regulator 30 includes a pair of plates 40 and 50 spaced in parallel with each other and urged with a bow spring 60 in a direction separating each other so as to move into engagement with the thin films 22 and 24 forming the flexible ink reservoir, respectively. An ink filter 18 is provided at a position inside the frame 16 and corresponding to the tip portion 13. The ink filter 18 is communicated with the ink reservoir by an appropriate porting element and includes an ink outlet communicated with the print head.
Under no stress conditions, the bow spring 60 is shaped as shown in solid lines of FIG. 7. When ink is fed outside the ink cartridge 10 from the ink reservoir, the thin films 22 and 24 move close to each other. Along with this movement, the side plates 40 and 50 of the pressure regulator 30 also move gradually so as to approach each other. Thereby, the side plates 40 and 50 and the bow spring 60 move to a mid point as shown by two-dot chain lines of FIG. 7. At this time, the bow spring 60 for urging the ink reservoir is compressed, so that the negative pressure level in the ink reservoir is increased.
In the ink cartridge configured as described above, if an external impact is directly transmitted to the thin films forming the ink reservoir, the thin film may be torn, causing ink leakage. This also applies large vibration to the ink stored in the flexible ink reservoir so that the ink supply to the head becomes unstable, which may cause printing nonconformity.